U.S. Funds Score Big by Betting Against Yen

Some of the biggest U.S. hedge-fund investors have made billions betting against the yen, exploiting Japan's determination to weaken its currency and boost its economy.

Wagering against the yen has emerged as the hottest trade on Wall Street over the past three months. George Soros, who made a fortune shorting the British pound in the 1990s, has scored gains of almost $1 billion on the trade since November, according to people with knowledge of the firm's positions. Others reaping big trading profits by riding the yen...